PASCO ME-9426A AMUSEMENT PARK PHYSICS - Manual (Page 11)

012-03776E Amusement Park Physics
7
Objective
In this lab you will experiment with centripetal accelerations on a playground merry-go-round.
Discussion
On a merry-go-round, we experience the sensation of being "thrown outward". Physics students know that this
is really inertia trying to keep us moving in a straight line. However, by exerting the right amount of inward or
centripetal force, we can successfully stay in a circular path (and on the merry-go-round). This force is usually
supplied by friction between our shoes and the ride and/or friction between our hands and the bars of the merry-
go-round. How does this force change with varying distance from the center of the ride? How does this force
depend on the speed of rotation of the ride?
At least two people are needed to carry out this lab, although three or more would be better. A stopwatch or digital
wristwatch and one or more horizontal accelerometers are needed to conduct the lab. Additionally, a measuring
device capable of measuring to the nearest 0.1 meter is needed.
Procedure
1. Measure off several distances from the center of rotation. Place the lateral accelerometer at one distance,
holding it against a bar if necessary to keep it from moving, and holding it so that it is level. The middle BB
should be at 0°. Record the distance, R, in Table 1. Note: Several riders, each with a lateral accelerometer,
could be positioned simultaneously at different distances.
2. Push the merry-go-round until it is moving at a steady, but relatively slow angular speed.
3. Measure the time it takes to go once completely around at the current speed, or better yet, the time to go five
times around and divide by five to get the average period of rotation, T. While the merry-go-round is turning,
the person on the ride measures the angle that the center BB moves to,
θ. Record the period and angle in Table 1.
4. Repeat step 3 with at least three different speeds of rotation, holding the accelerometer steady at the same
radius. Record the appropriate values in the data table.
5. Repeat step 3 after moving the accelerometer to a new radius. Try to rotate the merry-go-round at the same
speed it was turned during the first trial.
Analysis
1. For each trial, calculate the tangential speed, the speed that the accelerometer was travelling around its circular
path, v = 2 πR/T . Record your calculated values in Table 2.
2. For each trial, calculate the centripetal acceleration, a
c
= v 2 /R or a
c
= 4 π 2 R/T 2 .
3. For each trial, calculate the "measured acceleration" from the angle of the BB’s, a
c
= g tan θ.
4. Compare the calculated and the measured acceleration values for each trial. Were the results identical? Similar?
What type of percentage difference did you get in your results?
5. When the merry-go-round was going at approximately the same speed, how did the measured acceleration
vary with the radius? Was it linear? What was the mathematical relationship?
6. When the accelerometer was held at the same radius, what was the relationship between the measured
acceleration and the speed? Was it linear? What was the mathematical relationship?
7. Finally, what are some of the sources of possible error in this experiment? .
Experiment 1: Playground Physics / Merry-Go-Round